I've had a similar project sitting on my bench for about a year now, other things to work on...
Anyway, I got some 16 meg MP3 players surplus for $5 each, hold about three songs. Audioguru help me get it to play automatically when power is supplied. A LM386 audio amp wasn't loud enough at a reasonable solar powered battery option. So it sat for a while. Found some more surplus, a little amp with speakers for Gameboy $3.95, loud enough, but runs on a 9 volt battery, has a 6 volt adapter socket. Haven't gotten around to doing the 6 volt supply, solar charger, dark-activated switch, LM317 for the 1.5 volts to run the MP3 player. Anyway, pretty well worked it out, just not a lot of spare time for that one. Was kind of hoping to get an AVR microcontroller to work as the dark activated switch, so I could put a long delay on it, and switch it off when the song was done. Could also use it to start the player, and save some soldering.